This invention relates to stents used to maintain a body lumen, such as the prostatic urethra, and to systems for delivering stents into these body lumens.
Stents are a known class of medical device for expanding or maintaining an open lumen or passageway in various body cavities, vessels, or ducts. Stents have been employed, for example, in the urethra, the ureters, the biliary tract, the cervix, the rectum, the esophagus and blood vessels to relieve the pathological effects of constrictions occurring in these passageways.
Bladder obstruction arising from enlargement of the prostate gland in males is one of the most commonly encountered disorders in urology. The prostate gland lies under the bladder and surrounds the passageway known as the prostatic urethra, which transfers fluids from the bladder to the sphincter and ultimately outside the body. An enlarged prostate gland constricts the prostatic urethra leading to a condition known as benign prostatic hyperplasia (xe2x80x9cBPHxe2x80x9d). BPH causes a variety of obstructive symptoms, including urinary hesitancy, straining to void, decreased size and force of the urinary stream, and in extreme cases, complete urinary retention possibly leading to renal failure. A number of other irritating symptoms may also accompany BPH, including urinary frequency and urgency, nocturnal incontinence, and extreme discomfort.
Known stents used to combat BPH may not ensure patient safety and comfort. Indeed, existing stents, such as wire mesh stents, may become entangled with prostate tissue leading to infection and discomfort. Under such conditions, prostate tissue often penetrates the perforations of the wire mesh stent rendering it difficult, if not impossible, to remove without surgical intervention. Other devices, such as Foley catheters are retained in the bladder by a balloon inflated with sterile water or saline. This necessitates use of a collection bag to catch fluids drained from the bladder, thereby reducing a patient""s quality of life. In addition, many stents cannot accommodate unusually or abnormally shaped prostatic urethras or prostatic urethras of varying lengths and widths.
Also, internal forces from involuntary bodily functions (such as peristalsis and other secretory forces, as well as patient movement) may force some stents out of their intended position within the prostatic urethra. For instance, the bladder can exert intense pressure during urination, which tends to expel a stent positioned within the prostatic urethra. It is also possible that normal body motions, such as walking or running may displace a stent at this location.
In one embodiment, the invention reduces the risk of infection/inflammation, while also maintaining patient comfort and preventing migration of the stent out of the prostatic urethra. According to one feature, the outer surfaces of the stent are smooth, and do not become entangled with and/or potentially infect internal body tissue. Structural features of certain embodiments of the invention, including a double funnel or hourglass configuration, ensure that the stent will not dislodge or migrate out of its intended position. According to another feature the stent is easy to insert, and should circumstances warrant, easily removed without the need for invasive surgery. In addition, the stent may be designed according to the individual needs of particular patients by tailoring its dimensions to accommodate prostatic urethras of various sizes and shapes.
One aspect of the invention relates to a collapsible and expandable stent including first and second terminal ends spaced apart from each other, a substantially smooth wall disposed between the first and second terminal ends and a lumen extending between the first and second terminal ends. Preferably, the stent is designed for use in the prostatic urethra of a male patient, and is constructed of flexible biocompatible materials such as elastomeric compounds. Materials like these combine rigidity with the softness necessary for patient stability and comfort. To help retain the stent in place in a body of a patient, at least one of the first and second terminal ends is wider than at least some portion of the wall disposed between the terminal ends.
To further help anchor the stent in the body, the first and second terminal ends may further include a retention ring having an elastic member. Where both the first and second terminal ends include retention rings, these retention rings are preferably aligned in a substantially parallel relationship. By varying the size of the retention rings, the stent can accommodate prostatic urethras of different sizes and shapes. The retention rings may be constructed from the same elastomeric compounds used in the first and second terminal ends. According to one aspect, the rings incorporate an elastic member to provide rigidity to the device and to ensure that the device reverts spontaneously to its predetermined configuration from its collapsed state.
In one embodiment, both the first and second terminal ends are wider than at least some portion of the wall. Under this construction, the wall extending between the terminal ends forms a double funnel or hourglass configuration. Once placed in a patient, this double funnel configuration acts to maintain the stent in position within an open passageway. When placed in the prostatic urethra, for example, one of the first or second terminal ends rests at the bladder end of the prostatic urethra and allows for drainage of urine into the prostatic urethra. The other of the first or second terminal ends sits above the external sphincter to prevent migration into the bulbous urethra while maintaining drainage through the prostate.
A lumen may extend between the first and second terminal ends to allow drainage of fluids through the passageway. Alternatively or additionally, drainage may be provided or enhanced by grooves located on the wall. In addition, the wall may define one or more through-holes disposed along its length to provide for fluid communication with the lumen to further facilitate drainage.
In another embodiment, one of the first and second terminal ends further comprises a dome structure. The dome may define at least one aperture, and terminates in a protuberance. The wall of this embodiment may include at least one annular collar to provide breaking points for the device entering its collapsed state. To further enhance collapsibility, the wall may define one or more slots. The slots may comprise openings through, or concave surfaces along the wall.
According to one embodiment, the stent of the invention includes a coating material. The coating material may be disposed continuously or discontinuously on the surface of the stent. Further, the coating may be disposed on the interior and/or the exterior surface(s) of the stent.
The coating material may include, but is not limited to a medicinal composition that leaches into the wall of a body lumen after implantation (e.g. to deliver a therapeutic agent to the body lumen). The coating is preferably a polymeric material, which is generally provided by applying to the stent a solution or dispersion of preformed polymer in a solvent and removing the solvent. Suitable polymeric coating materials, include, but are not limited to polytetraflouroethylene, silicone rubbers, or polyurethanes, all of which are known to be biocompatible. Non-polymeric material may alternatively be used.
In another aspect, the invention is directed to a delivery system for inserting stents into a body of a patient. In general, the delivery system includes a retractable sheath, a shaft partially disposed within the sheath and a rotatable locking element disposed over the sheath.
According to one embodiment, the retractable sheath has a wall of a flexible material and proximal and distal portions. As used herein, xe2x80x9cdistalxe2x80x9d refers to an area or direction away from the medical operator inserting the device, while xe2x80x9cproximalxe2x80x9d refers to an area or direction close to the medical operator inserting the device into the patient. The retractable sheath defines an internal lumen that extends from the proximal to the distal portion. The internal lumen holds the stent in its collapsed state at the distal portion of the sheath. The sheath also defines a first groove and a longitudinal opening through the wall of the proximal portion. The first groove and longitudinal opening are connected and lie perpendicular to one another, forming an xe2x80x9cLxe2x80x9d or xe2x80x9cTxe2x80x9d shape.
Optional features of the sheath include a retraction handle, radiopaque locator bands, and a rounded distal end with a series of small longitudinal slits. The retraction handle may be disposed on the proximal portion of the sheath, and provides a grip to pull on to retract the sheath after insertion into a body of a patient. The radiopaque locator bands may be disposed on the wall of the sheath, and assist medical practitioners in positioning the stent under visualization by X-ray. The rounded distal end facilitates insertion of the stent in the urinary tract. The slits in the rounded distal end facilitate retraction of the sheath after insertion of the delivery system.
According to one embodiment, the shaft is coaxially disposed within the sheath and slidably movable within the lumen of the sheath. The shaft comprises at least one second groove. The shaft may further comprise an insertion handle, which provides a surface to push on to insert the delivery system into a body of a patient.
In a further embodiment, the rotatable locking element includes a tongue adapted to engage the first groove of the sheath and the at least one second groove of the shaft. The locking element is disposed over the proximal portion of the sheath.
When the tongue engages the first groove of the sheath and the at least one second groove of the shaft, relative movement between the sheath and the shaft cannot occur, thereby preventing premature deployment of the stent. To disengage the sheath from the shaft, the locking element is rotated, positioning the tongue in the longitudinal opening of the sheath. This allows relative movement between the shaft and the sheath, and thus allows retraction of the sheath over the shaft to deploy the stent. To disengage the tongue from the at least one second groove of the shaft, a thumb tab may be disposed on the locking element. Downward pressure on the thumb tab lifts the tongue out of the at least one second groove of the shaft. Releasing the tongue from the at least one second groove of the shaft allows the locking element to slide over the sheath.
The delivery system may include a slidable stop cup disposed on the sheath. The slidable stop cup is used to position the delivery system against the head of the penis of a male patient during insertion of the delivery system into the male urethra. Optionally, the slidable stop cup may be integrated with the locking element to stabilize or secure the positioning of the delivery system and the stent in the urinary tract.
In other aspects, the invention involves methods of placing stents, such as those previously described. One method of placing these and other collapsible and expandable stents into a body of a patient comprises collapsing the stent, inserting it into the distal portion of the sheath of the delivery system of the invention, inserting the delivery system into the body of the patient, retracting the sheath over the shaft, and removing the delivery system from the body of the patient, thereby deploying the stent within the body. An alternate method of placing the domed stent of the invention comprises providing the domed stent, positioning a conventional guidewire stylet assembly within the domed stent, inserting the guidewire stylet assembly into a body of a patient, and removing the assembly from the body of the patient, thereby deploying the domed stent within the body.
In another aspect, the invention involves methods for removing stents of the invention from a body of a patient after they have served their purpose. Removal of the stents of the invention comprises providing a cystoscope and a grasping device, inserting the cystoscope and grasping device into the body of the patient, locating the stent with the cytoscope, attaching the grasping device to the wall of the stent, removing the grasping device attached to the stent from the body, and removing the cystoscope from the body.
In yet another aspect, the invention involves methods of making the stents and delivery systems of the present invention. A method of making stents of the invention comprises injection molding the stent as one continuous piece. Alternatively, a method of making the domed stent comprises injection molding the body segment and proximal end segment in one mold, separately injection molding the dome in a second mold, and securing the individual components to one another. Similarly, a method of making the delivery systems of the invention comprises extruding the sheath, injection molding the other individual components and securing them together.
The foregoing and other objects, aspects, features, and advantages of the invention will become more apparent from the following description, the drawings, and from the claims.